Apparatus and method for large area chemical vapor deposition using multiple expanding thermal plasma generators

ABSTRACT

Chemical vapor deposition is performed using a plurality of expanding thermal plasma generating means to produce a coating on a substrate, such as a thermoplastic and especially a polycarbonate substrate. The substrate is preferably moved past the generating means. Included are methods which coat both sides of the substrate or which employ multiple sets of generating means, either in a single deposition chamber or in a plurality of chambers for deposition of successive coatings. The substrate surfaces spaced from the axes of the generating means are preferably heated to promote coating uniformity.

BACKGROUND OF INVENTION

[0001] This invention relates to plasma enhanced chemical vapordeposition. More particularly, it relates to deposition in an expandingthermal plasma (hereinafter referred to as “ETP”) system to coat largeareas of a substrate.

[0002] The use of ETP to deposit coatings, especially protectivecoatings, on substrates is known. For example, U.S. Pat No. 6,110,544describes a method of forming coatings on a plastic substrate such aspolycarbonate. The coatings that may be deposited include siliconoxide-based hardcoats, which can protect the plastic surface fromabrasion. Also capable of deposition are metal oxide-based coatings suchas zinc oxide. Coatings of these types are produced by introducing anorganosilicon or organometallic compound into an ETP and causing theplasma stream produced by said ETP to impinge upon the surface of thesubstrate. By using ETP, particularly those using equilibrium thermalplasma arc generators, high coating deposition rates may be achieved atrelatively low temperatures. It is particularly desirable that thesubstrate temperature be maintained lower than its glass transitiontemperature and/or softening temperature.

[0003] A problem with ETP deposition as described in the prior art isits incapability of efficiently producing a coating over a large area ofa substrate. A single ETP source typically coats an area of about 75-200cm². Thus, many passes of a substrate into contact with the ETP would benecessary to coat the entire surface thereof.

[0004] Various publications disclose coating apparatus and systems usinga plurality of coating units. For example, U.S. Pat No. 4,948,485discloses the disposition of a number of cascade arc plasma torches in acircular array around an axis, which may, for example, be a wire to becoated. Such a system is incapable being used to coat a single surfaceof, for example, a planar substrate.

[0005] U.S. Pat. Nos. 5,302,271 and 5,441,624 disclose multi-anodic arccoating systems in which the arcs are directed at a single surface of asubstrate. Anodic arcs are fundamentally different from ETP sources inthat they do not generate a thermal plasma and they use a consumableanode as the source material for deposition. In addition, those arcs areused for physical vapor deposition. As such, their operating parameters,such as arc-to-arc spacing, arc to substrate distance, and depositionpressure, are not adapted to ETP deposition.

[0006] It is of interest, therefore, to develop an apparatus and methodsuitable for coating relatively large areas of a substrate by ETPdeposition. In particular, an apparatus and method that is adaptable tovarious configurations of substrates and to the particular parameters ofETP systems is desirable.

SUMMARY OF INVENTION

[0007] The present invention provides an ETP coating apparatus andprocess particularly adapted to efficiently coat large substrates. Theinvention can be configured so as to provide coatings having desirableproperties, including uniformity and reproducibility.

[0008] One aspect of the invention is to provide a substrate coatingapparatus. The apparatus comprises: a deposition chamber adapted to bemaintained at subatmospheric pressure; support means in the depositionchamber for a substrate, the substrate having at least one surface; anda set of expanding thermal plasma generating means associated with thedeposition chamber, the generating means being adapted to deposit acoating on the substrate. The set comprises at least two expandingplasma generating means, with all of the means in the set beingcodirectionally oriented.

[0009] Another aspect of the invention is to provide a method forcoating a substrate. The method comprises generating a set of at leasttwo expanding thermal plasma plumes to deposit a coating on saidsubstrate, wherein each of the plumes in the set is codirectionallyoriented.

BRIEF DESCRIPTION OF DRAWINGS

[0010]FIG. 1 is a schematic view of an illustrative substrate coatingapparatus of the invention, in which ETP generating means are locatedoutside the deposition chamber;

[0011]FIGS. 2 and 3 are illustrative configurations of ETP generatingmeans according to the invention;

[0012]FIG. 4 is a schematic cross-sectional view of an ETP generatingmeans useful in the invention;

[0013]FIGS. 5 and 6 are views of embodiments of the invention in whichheating elements are respectively located between and upstream of theETP generating means;

[0014]FIG. 7 is a view of an embodiment in which the substrate is coatedsimultaneously on both sides;

[0015]FIG. 8 is a view of an embodiment adapted to coat a curvedsubstrate;

[0016]FIGS. 9 and 10 are orthogonal views of an embodiment includingseveral coating units according to the invention;

[0017]FIG. 11 is a cross-sectional view of an embodiment including ashutter between the ETP generating means and the substrate, as well asan alternative substrate support means; and

[0018]FIGS. 12A and 12B are orthogonal views illustrating theconfiguration of Examples 5-8.

DETAILED DESCRIPTION

[0019] An embodiment of the substrate coating apparatus of the presentinvention is shown in FIG. 1. It includes deposition chamber 10 equippedwith vacuum-producing means 14, such as a vacuum pump. Substrate supportmeans 11, which may be a hook, frame, arm, clamp, or the like, holdssubstrate 12. As shown in FIG. 1, support means 11 is attached tomovement actuator 13, described hereinafter, so that substrate 12 can bemoved perpendicular to the plane of the figure; i.e., in and/or out ofsaid plane. However, it is also within the scope of the invention forsupport means 11 to be fixed in position within deposition chamber 10.

[0020] Substrate 12 is shown as a planar (i.e., flat) object in FIG. 1,but it is also contemplated for substrate 12 to be curved or ofirregular shape, as described hereinafter. In general, however,substrate 12 will have a substantial width dimension, typically at leastabout 25 cm and preferably at least about 50 cm. That is, it ispreferably not a wire, which is essentially a one-dimensional object.For the most part, the length dimension of the substrate will also be atleast about 25 and most often at least about 100 cm.

[0021] The substrate may be of any suitable material including metal,semiconductor, ceramic, glass or plastic. In a preferred embodiment, itis a thermoplastic such as polycarbonate, copolyestercarbonate,polyethersulfone, polyetherimide or acrylic. Polycarbonate isparticularly preferred; the term “polycarbonate” in this contextincluding homopolycarbonates, copolycarbonates andcopolyestercarbonates.

[0022] Associated with (i.e., in FIG. 1, outside but in effectivecommunication with) deposition chamber 10 are ETP generating means 15.According to the invention, a plurality of said means are present; twoare shown in the figure, but there may and frequently will be more thantwo, for example up to about 12. ETP generating means 15 may also bewholly within said deposition chamber. Typically, each of said ETPgenerating means has provision for independent adjustment of spacing,distance to substrate, and reagent feed.

[0023] Each ETP generating means shown in FIG. 1 is fitted with plasmanozzle 16 (although a nozzle is not a required aspect of the invention),whereby plumes 17 of plasma are produced which contact one side ofsubstrate 12. Each plume 17 has a central axis 18 and said central axesare spaced from each other from each other at a distance D. As shown,plumes 17 intersect each other and there is an area of the substratecontacted by both plumes, and this will generally be the case asdescribed in detail hereinafter.

[0024] All of the ETP generating means in a set are codirectionallyoriented, i.e., they point in the same direction so as to produce plasmaplumes in the same direction. It is, however, within the scope of theinvention to employ more than one set of ETP generating means. Forexample, two sets oriented in opposite directions can be employed oneither side of a substrate in the form of a sheet, whereby coatings onboth sides of said sheet are produced.

[0025] The ETP generating means in any set thereof are oriented so thatthe plasmas produced thereby will impinge on the substrate and produce acoating thereon. Thus, they generally point toward a side of thesubstrate; for example, such that the central axes of the plasmas areperpendicular to the substrate when the substrate is flat and in ananalogous configuration for curved and/or irregular shaped substrates.Beyond that, certain highly preferred orientation parameters have beendiscovered and are described in detail hereinafter. Preferably, however,the substrate support means is attached to movement actuator 13, such asa pull cord or ribbon, a rail, a screw rod, or one or more wheels orbearings, any of which may be powered by a motor (not shown), wherebythe substrate may be moved past the set of ETP generating means forefficiency of coating. As shown in FIG. 1, substrate 12 will move in aplane perpendicular to that of the figure. It may move into and out ofdeposition chamber 10 through appropriate openings 23 in the walls ofsaid chamber.

[0026] Particularly when a movement actuator is present, the ETPgenerating means in a set may be in a straight line parallel to theplane of motion of the substrate, as shown in FIG. 2, in which four suchmeans are in a straight line represented by the dashed line in saidfigure, and with the center axes of the plasma plumes produced by saidETP generating means oriented perpendicular to the plane of motion ofthe substrate support means. They may also be in a zigzag configurationin a plane parallel to said plane of motion, as shown in FIG. 3, inwhich seven such means are so arranged. The angle between successivelines leading from one ETP generating means 15 to the next is typicallyin the range of about 10-80°, and preferably about 30-60°.

[0027] In each of FIGS. 2 and 3, the plane of motion of the substrate isspaced from that of the figure and its direction of motion is from leftto right. Other configurations are also contemplated. For example, adome-shaped substrate may be coated with a set of ETP generating meansin a circular array, but in that instance it may be preferable not tomove the substrate during the coating operation.

[0028]FIG. 4 shows one suitable design for ETP generating means 15, saidmeans being classified as a wall-stabilized DC arc generator. It shouldbe understood, however, that other designs are possible and that theembodiment of FIG. 4 is only illustrative.

[0029] Said embodiment includes at least one cathode 413, plasma gassupply line 417, and anode 419. Typically, more than one cathode 413 ispresent. Cathode(s) 413 may comprise tungsten or thorium-doped tungstentips and may be surrounded by cathode housing 405 to isolate cathode 413from the walls of cathode support plate 428 and to provide for watercooling. Cathode housing 405 may comprise a shell surrounding anisolating mantle made from an insulating material such as polyvinylchloride or polytetrafluoroethylene.

[0030] Cathodes 413 are separated from anode 419 by at least one cascadeplate 426, preferably comprising copper discs containing a centralaperture having a shape corresponding to that of the anode aperture.

[0031] Optionally, cathode(s) 413 may also contain a purging gas supplyline adjacent to plasma gas supply line 417 to supply a purging orflushing gas, such as argon, prior to supplying a plasma gas.

[0032] Referring again to FIG. 4, ETP generating means 15 also containsat least one plasma gas supply line 417. To form a plasma, at least oneplasma gas is supplied through said plasma gas supply. The plasma gasmay comprise a noble gas, nitrogen, ammonia, or hydrogen, for example,or any combination thereof, with argon often being preferred. If thereis more than one plasma gas, then the plural gases may either besupplied through plural supply lines or may be premixed before beingsupplied to line 417. Referring again to FIG. 1, the plasma gas in ETPgenerating means 15 is maintained at a higher pressure than the pressurein deposition chamber 10, which is continuously evacuated by a pump. ADC voltage is then applied between cathode(s) 413 and the anode 419 togenerate a plasma in ETP generating means 15. The plasma is then emittedas a supersonic plasma via the anode 419 aperture and expanded as aplasma plume into deposition chamber 10 due to the pressure differencebetween deposition chamber 10 and ETP generating means 15.

[0033] The cathode support plate 428 is attached to cascade plate(s) 426and anode 419 by insulated bolt 427 or by equivalent fasteners. Cascadeplate 426 is electrically insulated from cathode support plate 428 andanode 419 by spacers 415 comprising an electrically insulating materialthat can withstand elevated temperatures. For example, spacers 415 maycomprise O-ring vacuum seals, polyvinyl chloride rings, boron nitriderings or the like.

[0034] Plasma discharge at high power density and high temperature tendsto heat cascade plate(s) 426 and anode 419. Preferably, therefore,cascade plate(s) 426 and anode 419 contain coolant channels 429 and 440,respectively. The channels 429, 440 typically have a circular shapewithin the bulk of plate(s) 426 and anode 419. Coolant, such as chilledwater supplied through a water supply line 406, flows through channel440 to cool the anode 419 during operation. A similar water supply line(not shown) is provided to supply water to channel 429.

[0035] Nozzle 418 is preferably attached to or mounted on anode 419.Alternatively, nozzle 418 can be formed onto anode 419 as one contiguousunit.

[0036] Nozzle 418 can optionally further include an integral orremovable divergent portion, referred to as a nozzle extension 439, forconfinement and further directing of the plasma and reactive speciesflow.

[0037] Reagent supply lines 412, 414 and 416 are in fluid communicationwith nozzle 418. Nozzle 418 typically includes one or more injectorscoupled to reagent supply line(s) 412, 414, and 416 providing for thedelivery of reagents into the plasma. The injectors may include ringshaped reagent supply channels connected to injection holes or aslit-shaped injector. For example, as shown in FIG. 4, reagent supplyline 414 connects to reagent supply channel 435 formed inside the bodyof nozzle 418. Reagent supply channel 435 contains a plurality ofopenings 434, which are preferably evenly distributed around thecircumference of channel 435. The reagent flows in several directionsfrom line 414 into channel 435 and then simultaneously through openings434 into the nozzle. Likewise, supply line 416 is connected to channel433 and openings 432 and supply line 412 is connected to channel 431 andopenings 430.

[0038] The reagents are supplied to the plasma through supply lines 412,414, 416, but it will be understood that more or fewer supply lines andassociated structure elements may be present, depending on the chemistryof the desired plasma. For example, oxygen gas may be supplied throughline 414, zinc may be supplied through line 416, and indium may besupplied through line 412 to form an indium zinc oxide film on substrate12. Line 416 may be sealed and oxygen and zinc supplied if a zinc oxidefilm is to be deposited. Illustrative reagents include oxygen, nitrousoxide, nitrogen, ammonia, carbon dioxide, fluorine, sulfur, hydrogensulfide, silane, organosilanes, organosiloxanes, organosilazanes andhydrocarbons for making oxide, nitride, fluoride, carbide, sulfide andpolymeric coatings. Examples of other metals whose oxides, fluorides,and nitrides may be deposited in the same way are aluminum, tin,titanium, tantalum, niobium and cerium. Alternatively, oxygen andhexamethyldisiloxane, tetramethyldisiloxane oroctamethylcyclotetrasiloxane may be supplied to form a silica-basedhardcoat. Other types of coatings which can be deposited by ETP will beapparent to those skilled in the art.

[0039] It has been discovered that, for each ETP generating means, thecoating deposition characteristics vary spatially according to a bellcurve, with the maximum of the curve corresponding to the central axisof the ETP generating means. Examples of such characteristics aresubstrate temperature rise due to plasma exposure and the thickness ofthe coating produced. A temperature profile is produced because thecenter portion of a plasma plume has a higher plasma density and thermalload than the edge portions thereof. As an illustration of thisvariation in deposition properties, a polycarbonate substrate maytypically vary in temperature by about 10-30° C. from the central axisto the edge portion of a single plasma plume.

[0040] One embodiment of the invention, therefore, includes at least oneand preferably a plurality of temperature control means located andadapted to heat regions of the substrate spaced from the central axes ofthe ETP generating means. When heating means are employed, they may beof any type; examples are infrared heaters (i.e., heat lamps), microwaveheaters, resistance heaters and non-reactive plasma streams. The powersupplied to the heating means is preferably effective to maintain asubstantially uniform substrate temperature, the term “substantiallyuniform” meaning a temperature difference over the substrate area ofabout 10° C. or less, preferably about 6° C. or less.

[0041] The heating means are preferably located within the depositionchamber, for example, between the ETP generating means and normally atthe halfway point, to provide simultaneous deposition and heating. It isoften preferred, however, to locate the heating means upstream (withrespect to substrate movement) from the ETP generating means, or even ina separate preheating chamber. When so located, they will ordinarily becentered on a line extending parallel to the downstream motion of thesubstrate to a point halfway between the ETP generating means.

[0042] Illustrative configurations of apparatus of the inventionincluding heating means are depicted in FIGS. 5 and 6. In FIG. 5, twoETP generating means 15 and three heating elements 520 are located indeposition chamber 10. The heating elements are located on either sideof and between the ETP generating means, so as to provide simultaneousdeposition and heating with the heated regions being on either side ofthe central axes of the plasma plumes. FIG. 6 shows a differentarrangement in which three heating elements 620 are located upstreamfrom two ETP generating means 15 (substrate movement being from left toright in a plane parallel to that of the figure) but within depositionchamber 10.

[0043] Spacing of the ETP generating means also has an effect on theuniformity of the coating deposited on the substrate. In order tomaximize uniformity, it is preferred to provide a spacing such thatthere is overlap between the edge portions of the plurality of plasmaplumes. The precise amount of overlap will depend on numerous factors,such as the size of the plasma produced by the ETP generating means, thedistance of the ETP generating means from the substrate, power to theETP generating means, and flow rates of various reagents. It is arelatively simple matter to determine by simple experimentation theoptimum spacings for each coating apparatus. It is often found, forexample, that excellent results are obtained when the anode (as shown inFIG. 4) of each ETP generating means is about 20-40 cm and especiallyabout 25-28 cm from the substrate at a chamber pressure of about 30 toabout 60 millitorr. The spacing (D in FIG. 1) between center axes of theETP generating means is generally about 10-21 cm and especially about12-18 cm for wall-stabilized DC arc plasma generators operated at apressure of about 200-800 torr.

[0044] The apparatus depicted in FIG. 1 is adapted to coat only one sideof a substrate a single time. The invention includes, however, coatingmore than one side at once, as well as depositing successive coatings.An illustrative apparatus for this purpose is shown in FIG. 7. Itincludes deposition chamber 10, substrate 12 and eight ETP generatingmeans 15 of which only the four top ones are visible, the other fourbeing immediately below the ones shown. Each ETP generating means shownin FIG. 7 includes nozzle 730, the word “nozzle” as used in this contextincluding any nozzle extension (439 in FIG. 4). Substrate 12 moves inthe direction of the arrow whereupon plasma plumes 721, 722 formcoatings 703 and 704 on opposite sides of substrate 12, and plasmastreams 723, 724 form superimposed coatings 705 and 706.

[0045] While the substrate in FIG. 1 is shown as planar, the apparatusdepicted in that figure may also be employed to coat an object having acurved surface, provided said surface is nearly planar; i.e., itscurvature is slight or only parts thereof are curved. However, amodification of the apparatus, which may advantageously be employed tocoat articles with a higher curvature, is shown in FIG. 8.

[0046] Curved substrate 812 in FIG. 8 again moves in a planeperpendicular to that of the figure, and enters and exits depositionchamber 10 through openings 23. Eight PECVD means 15 produce plasmaplumes which form coatings 3 and 4 on opposite sides of substrate 812.Nozzles 830 are of varying lengths so that they produce a distance ofconstant length between the end of the nozzle and curved substrate 812.Further, nozzles 830 may have successive portions of unequal lengthwith, for example, the upper portions of the nozzles at the top of thefigure being shorter than the lower portions.

[0047] The configuration shown in FIG. 8 includes placement of theanodes of the ETP generating means at a constant distance from thecurved substrate. Alternatively, ETP generating means which includenozzles with variation in plasma generation conditions may be used,producing equivalent effects on the various portions of the substrate atdifferent distances from the anodes.

[0048] It is also contemplated to provide for motion of the plasmaplumes impinging on the substrate, so as to scan a region of thesubstrate, This may be achieved by mounting the ETP generating means orthe nozzles associated therewith on swivels that may be manually orcomputer controlled. It may also be achieved by mounting one or moremagnets on or near the walls of the deposition chamber, therebypermitting magnetic variation of the direction and shape of the plasmaplume.

[0049] One preferred embodiment of the invention includes the use of aplurality of deposition chambers and sets of ETP generating means fordeposition of plural coating layers on a substrate. FIGS. 9 and 10 areorthogonal cross-sectional views of an illustrative apparatus for suchdeposition. Of course, such an apparatus will most often employ a singlesubstrate support means and movement actuator adapted to convey saidsubstrate through said deposition chambers in succession.

[0050] In FIGS. 9-10, there are shown three deposition chambers 901, 902and 903. Each of said chambers is shown as containing eight ETPgenerating means 15, four on each side of the substrate (although thenumber thereof is not critical), with each of said ETP generating meanshaving a nozzle, one of said nozzles being designated 916. Each pair ofdeposition chambers is connected by a pump port 924, and the input andoutput ends of the system are attached to load locks, 925 and 926. Theseitems provide for removal of gases, to maintain subatmospheric pressurein the chamber, and for sample loading and unloading. Substrates 12, twoin number as shown, move through the system from left to right as shownby the arrows, receiving three successive coatings in the threedeposition chambers.

[0051] It will be apparent that the multiple chamber apparatusillustrated in FIGS. 9-10 can be modified in various ways. For example,one or more ETP generating deposition chambers may be replaced bychambers designed for deposition of coatings by sputtering, evaporation,chemical or physical vapor deposition or the like, or by non-coatingplasma treatment chambers. Also, pump ports 924 and load locks 925 and926 may be replaced or supplemented by conventional heating,pretreatment, or post-treatment units.

[0052] A further feature of the invention which may preferably beemployed under certain conditions is shown in FIG. 11. It is a shutter1105 situated in deposition chamber 10 between substrate 12 and the ETPgenerating means (not shown), said shutter being positioned by handle orpositioning means 1107. Said shutter contains one or more apertures 1106configured so as to allow overlapping of adjacent plasma plumes butblock the relatively low power edge portions of said plumes. Also shownin FIG. 11, is substrate support means 1111 comprising a flat panelwhich provides support for the entire substrate, which is attached tomovement actuator 13 and which may be used if only one side of thesubstrate is to be coated.

[0053] The invention is illustrated by the following examples.

EXAMPLE 1

[0054] A flat substrate, 30×30 cm, of a commercially available bisphenolA polycarbonate, coated with a chemically deposited silicone hardcoat,was vertically mounted in a deposition chamber of a coating apparatuscontaining two ETP generating means. The working distance between theanodes of the ETP generating means and the substrate was 36 cm, thecenter-to-center spacing between the ETP generating means was 19 cm, andthe effective scanning width of the deposition was about 30 cm.

[0055] The deposition chamber was evacuated to a pressure of less than 5millitorr, and an argon plasma plume was generated by flowing argonthrough the arcs in the ETP generating means and applying a directcurrent between the cathodes and anodes thereof while maintainingdeposition chamber pressure at about 35 millitorr. Oxygen was injectedinto the argon plasma and the substrate was exposed to the argon-plasmaplume in a plasma pretreatment step. The substrate was scanned threetimes in a vertical direction past the ETP generating means.

[0056] A tetramethyidisiloxane (TMDSO) precursor vapor was then suppliedto the argon-oxygen plasma plume to deposit a silica-based coating 3 onthe substrate. An argon-oxygen plasma post-treatment step was carriedout after the deposition step.

[0057] The thickness of the coating was measured at five points at thecenter and the corners of each of seven 10×10-cm sections of thesubstrate, using a Dektak profilometer. Also measured, at midpoints ofthe sides of each section, was the Taber haze increase, which is ameasure of abrasion resistance of the sample; it was measured bydetermining the initial haze of the coated sample using a Gardner hazemeter, rolling a pair of CS-10F wheels with 500-g load each 1000 timesin a circle over the sample and measuring the haze (in percent) afterthe wheel rolling step. Coating thickness was 2.6 micron in average witha standard deviation of 0.2 micron. The average Taber haze increase was2.8% with a standard deviation of 0.4. Control panel sections which hadnot been coated showed a Taber haze increase in the range of about12-16%. Thus, the abrasion resistance of the coating produced by themethod of the invention was demonstrated.

EXAMPLE 2

[0058] The procedure of Example 1 was repeated, except that a curvedsubstrate, adapted for use as an automobile window, was employed. Theincrease in Taber haze was measured at the centers of each side of five10×10-cm sections of the substrate. The average increase was 2.7% with astandard deviation of 0.4%. Thus, the method of the invention was shownto be effective on curved as well as flat substrates.

EXAMPLE 3

[0059] The procedure of Example 1 was repeated, except that an array ofthree ETP generating means, arranged in a zigzag configuration, wasemployed. The ETP generating means were arranged so that the verticaldistance between the centers of the plasma plumes was 15 cm and thehorizontal distance was about 26 cm. A retractable shutter having anaperture 20 cm wide was placed between the ETP generating means and thesubstrate.

[0060] Coating thicknesses and Taber haze increases were measured as inExample 1 Thicknesses were 4.1 micron in average with a standarddeviation of 0.4 micron. The average Taber haze increase was 1.9% with astandard deviation of 0.3%.

EXAMPLE 4

[0061] The procedure of Example 3 was repeated, with the exception thata curved substrate, adapted for use as an automobile window, wasemployed. The average Taber haze increase was 2.3% with a standarddeviation of 0.5%.

EXAMPLES 5-8

[0062] These examples illustrate the effects of operating variables oncoating properties and performance. The experimental setup isillustrated in FIGS. 12A and 12B. Three 10×30-cm flat bisphenol Apolycarbonate subpanels 1212L, 1212M, 1212R respectively were mounted assubstrates on a threefold substrate panel with an incline angle of 10°between adjacent subpanels, said panel being generally in the plane ofthe paper. Two wall-stabilized DC arcs 15, located in a plane beneaththat of the paper, were used as the ETP generating means for thedeposition of a coating on one side of substrates 1212 using anargon-oxygen-octamethylcyclotetrasiloxane (“D4”) plasma, and moving thesubstrates from top to bottom as indicated by the arrow in FIG. 12A.Subpanels 1212L and 1212R were mainly exposed to the center portions oftwo plasma plumes 17, while subpanel 1212M was mainly exposed to theoverlap portion 1218 of the plumes. After being coated, the substrateswere cut into 10×10-cm coupons for Taber and thickness measurements.Deposition conditions and coating performance are given in Table 1.TABLE I Example 5 6 7 8 Spacing between arcs, cm 21 21 17 17 Distance,anode to substrate, cm 35 26 26 26 Current, amp 75 50 75 75 Chamberpressure, mtorr 30 60 30 30 Argon feed rate, slm 2.4 1.4 2.4 1.4 Oxygenfeed rate, slm 1.2 1.2 1.2 1.2 D4 vapor feed rate, slm 0.2 0.4 0.4 0.2Scan rate, cm/sec 1.4 0.3 3.3 0.8 Coating thickness, microns: L 1.7 5.51.3 3.1 M 2.0 2.4 2.0 3.5 R 1.7 5.9 1.3 3.1 Taber haze increase, %: L 172.0 12 1.7 M 2.7 15 10 2.0 R 21 1.1 12 2.2

[0063] It is apparent that coatings can have non-uniform performanceover the area. Taber haze increase can be high on sub-panels L and R,but low on M (Example 5); or the opposite (Example 6). Coatings can haveuniform but poor Taber performance (Example 7), or uniformly good Taberperformance (Example 8). Operating variables given in Table 1 have beenfound to be very important with respect to achieving coating performanceusing the ETP deposition method of the invention. Variables such asreagent and gas feed rates are associated with CVD processes only, andwould be totally irrelevant to a PVD process such as the anodic arc.

EXAMPLES 9-12

[0064] A two-source linear array was used to deposit a coating similarto that of Example 1 on flat bisphenol A polycarbonate substrates. Thesubstrates were supported on either a flat or, to simulate curvedsurfaces, a curved substrate holder. Three 10.2×30.5-cm substrates,forming a 30.5×30.5-cm total area, were coated. A vacuum chamber with aninternal substrate scanning mechanism was used. The coating proceduretypically included the steps of loading the substrate into thedeposition chamber, pumping down the deposition chamber to vacuum,preheating the substrate to the desired temperature profile, using anETP source to generate a plasma plume containing the depositionreagents, scanning the substrates to deposit coatings thereon,extinguishing the ETP source, venting the deposition chamber andunloading the substrate.

[0065] The substrates were preheated with infrared heaters, which werelocated as illustrated in FIG. 6. They were then coated with twosilica-based hardcoats at a distance of 25.5 cm from the anodes of theETP generating means. The Taber haze increase was measured at fourpoints on each of three 10.2×10.2 sections of each substrate.

[0066] TABLE II lists the preheating conditions. Temperatures are indegrees C. The term “Preheat/center” indicates a preheating temperaturein a substrate region to be irradiated by the center portions of theplasma streams. The term “Preheat/overlap” indicates a preheatingtemperature in a substrate region to be irradiated by an overlap of theedge portions of the plasma streams. The term “Deposition temp./center”indicates the deposition temperature of substrate regions irradiated bythe center portions of plasma streams. The term “Depositiontemp/overlap” indicates the deposition temperature of the substrateregion irradiated by the overlap of the edge portions of plasma streams.Thus, the terms “Deposition temp.” denote the temperatures resultingfrom the heat retained from the preheating step and the heating of thesubstrate by the plasma streams. The terms “Taber/center” and“Taber/overlap” refer to the Taber haze increase, in percent, in theregions of the substrate irradiated by the center and the overlap of theplasma streams, respectively. The preheating temperature was measured bythermocouples placed in the array. TABLE II Preheat/ Preheat/ DepositionDeposition Taber/ Taber/ Example center overlap temp./centertemp./overlap center overlap 9  85  85 133 103 3 10  10 100 100 146 1162.5 5 11  85 110 149 147 3 3 12 114 130 160 155 2 2

[0067] It will be apparent that the uniform center-overlap preheatingconditions of Examples 9 and 10 resulted in substantial variation indeposition temperature (about 30° C.) and did not afford satisfactoryTaber values. In Example 5, for instance, the difference in Taber variedfrom 3 to 10. In contrast, the differential heating conditions ofExamples 11 and 12, in which preheat temperature variations of 15° and16° C. resulted in relatively constant deposition temperatures varyingonly in the range of 2-5° C., afforded very uniform Taber values.

[0068] Those skilled in the art will understand that the most favorablepreheating and deposition conditions will vary with the substrate beingcoated and the coating conditions. For any given set of conditions, theycan be determined by simple experimentation.

[0069] While typical embodiments have been set forth for the purpose ofillustration, the foregoing descriptions and examples should not bedeemed to be a limitation on the scope of the invention. Accordingly,various modifications, adaptations, and alternatives may occur to oneskilled in the art without departing from the spirit and scope of thepresent invention.

1. A substrate coating apparatus comprising: a deposition chamberadapted to be maintained at subatmospheric pressure; support means insaid deposition chamber for a substrate, said substrate having at leastone surface; and a set of expanding thermal plasma generating meansassociated with said deposition chamber, said generating means beingadapted to deposit a coating on said substrate, said set comprising atleast two of said means and all of said means in said set beingcodirectionally oriented.
 2. The apparatus according to claim 1, whereinthe expanding thermal plasma generating means are wall-stabilized DC arcgenerators.
 3. The apparatus according to claim 1, wherein saidexpanding thermal plasma generating means are within said depositionchamber.
 4. The apparatus according to claim 1, wherein said expandingthermal plasma generating means are outside but in communication withsaid deposition chamber.
 5. The apparatus according to claim 1, furthercomprising a movement actuator adapted to move the substrate supportmeans past said set of expanding thermal plasma generating means.
 6. Theapparatus according to claim 1, wherein the substrate support means is ahook, frame, arm or clamp.
 7. The apparatus according to claim 1,wherein the substrate support means is a flat panel adapted to providesupport for the entire substrate.
 8. The apparatus according to claim 1,further comprising a shutter in said deposition chamber between saidsubstrate support and said expanding thermal plasma generating means,said shutter containing one or more apertures configured so as to allowoverlapping of adjacent plasma plumes but block the low power edgeportions of said streams.
 9. The apparatus according to claim 3, whereinthe expanding thermal plasma generating means are in a straight lineparallel to the plane of motion of the substrate support means, and withthe center axes of the plasma plumes produced by said expanding thermalplasma generating means oriented perpendicular to the plane of motion ofthe substrate support means.
 10. The apparatus according to claim 3,wherein the expanding thermal plasma generating means are in a zigzagconfiguration in a plane parallel to the plane of motion of thesubstrate support means, and with the center axes of the plasma plumesproduced by said expanding thermal plasma generating means orientedperpendicular to the plane of motion of the substrate support means. 11.The apparatus according to claim 10, wherein the angle betweensuccessive lines leading from one expanding thermal plasma generatingmeans to the next is in the range of 10-80°.
 12. The apparatus accordingto claim 1, further comprising at least one temperature control meanslocated and adapted to heat or cool substrate regions spaced from thecenter axes of the expanding thermal plasma generating means.
 13. Theapparatus according to claim 12, wherein said temperature control meansare heating means.
 14. The apparatus according to claim 12, wherein saidtemperature control means are located on either side of and between theexpanding thermal plasma generating means.
 15. The apparatus accordingto claim 14, wherein said temperature control means are locatedupstream, with respect to movement of the substrate support means, fromthe expanding thermal plasma generating means.
 16. The apparatusaccording to claim 1, wherein the expanding thermal plasma generatingmeans are located such that the anodes thereof are at a distance of20-40 cm from the substrate.
 17. The apparatus according to claim 16,wherein the expanding thermal plasma generating means are spaced so thattheir center axes are about 10-21 cm apart.
 18. The apparatus accordingto claim 1, wherein the apparatus comprises a plurality of sets ofexpanding thermal plasma generating means, located to deposit coatingson more than one side of a substrate.
 19. The apparatus according toclaim 1, wherein the apparatus comprises a plurality of sets ofexpanding thermal plasma generating means, located to deposit successivecoatings on a substrate.
 20. The apparatus according to claim 1, whereinthe locations and configurations of said expanding thermal plasmagenerating means are adapted to deposit a coating on a curved substrate.21. The apparatus according to claim 1, wherein the apparatus comprisesa plurality of deposition chambers and sets of expanding thermal plasmagenerating means, for deposition of plural coating layers on asubstrate.
 22. A substrate coating apparatus comprising: a plurality ofdeposition chambers, each of said chambers adapted to be maintained atsubatmospheric pressure; support means adapted to convey a substratethrough said deposition chambers in succession; a movement actuatoradapted to move said substrate support means and substrate through saiddeposition chambers in succession; a plurality of sets of expandingthermal plasma generating means associated with said depositionchambers, said generating means being adapted to deposit a coating onsaid substrate, each of said sets comprising at least two of said meansand all of said means in each of said sets being codirectionallyoriented; said generating means in each set being oriented in a straightline or a zigzag configuration, said line or configuration beingparallel to the plane of motion of the substrate support means, and saidgenerating means being located such that the anodes thereof are at adistance of about 20-40 cm from the substrate and spaced so that theircenter axes are about 10-21 cm apart; and heating means located andadapted to heat substrate regions spaced from the center axes of saidgenerators.
 23. The apparatus according to claim 22, wherein a pluralityof sets of expanding thermal plasma generating means are located todeposit coatings on more than one side of a substrate.
 24. A method forcoating a substrate, the method comprising generating a set of at leasttwo expanding thermal plasma plumes to produce plasma enhanced chemicalvapor deposition or PECVD of a coating on said substrate, each of saidplumes in said set being codirectionally oriented.
 25. The methodaccording to claim 24, wherein the substrate is a thermoplasticsubstrate.
 26. The method according to claim 25, wherein thethermoplastic is a polycarbonate.
 27. The method according to claim 24,wherein the plasma is an argon or argon-oxygen-organosiloxane plasma.28. The method according to claim 27, wherein the coating issilica-based.
 29. The method according to claim 24, wherein thesubstrate is moved past at least one set of expanding thermal plasmagenerating means.
 30. The method according to claim 24, whereinsubstrate regions spaced from the center axes of expanding thermalplasma generating means producing said coating are heated prior to orsimultaneously with the coating operation.
 31. The method according toclaim 24, wherein a plurality of sets of plasma plumes is generated todeposit coatings on more than one side of said substrate.
 32. The methodaccording to claim 24, wherein a plurality of sets of plasma plumes isgenerated to deposit successive coatings on said substrate.
 33. Themethod according to claim 24, wherein the substrate is planar.
 34. Themethod according to claim 24, wherein the substrate is curved.
 35. Amethod for coating a polycarbonate substrate, the method comprisinggenerating a plurality of sets of at least two expanding thermal plasmaplumes to produce successive coatings on said substrate while movingsaid substrate past said sets of plumes, each of said plumes in said setbeing codirectionally oriented; said coatings being silica-based and theplasmas being argon or argon-oxygen plasmas.
 36. An article coated bythe method of claim 24.